Electric oven



A. u. GRAPP. ELECTRIC oven. APPLICATION FILED MAYZhjQZT- Patented Feb. 14, 1922.

s SHEETS-SHEET 1.

UNITED s'rA'rEs PATENT OFFICE.

ALBERT E. GRAPP, OF MINNEAPOLIS, MINNESOTA.

' ELECTRIC OVEN.

To all whom it may con cern Be it known that I, ALBERT, E. (irRArP, a citizen of the United States, residing at Minneapolis, in the county of Hennepin and State of Minnesota, have invented eer-' tain new and useful Improvements in Electric Ovens; and I do hereby declare the fol.- lowing to be a full, clear. and exact description of the invention. such as will enable others skilled in the art to which it appertains to make and use the same.

' the claims.

' A commercial form of this'improved oven is illustrated in the accompanying drawings,

wherein like characters indicate like parts throughout the several views.

Referring to the drawings:

Fig. l is a perspective showing the oven wall of each oven section is provided with 80 made up of a plurality of sections or units;

Fig. 2 is a horizontal section taken through one of the oven sections or. units; Fig. 3 is a vertical section taken longitudinally through one of the oven sections or units and showing also fragments of other sections or units, one above and one below the same;

Fig. A is a fragmentary view in front elevation, showing a port10n otone of the oven sections and particularly illustrating the door and latch structure;

Fig. 5 is a section taken on the line'5-5 of Fig. 4; y

Fig. 6 is a fragmentary vertical section of the oven and showing a light bulb with in. a light box and the door-actuating cir cuit-controlling switch to said bulb;

Fig. 7 is a perspective showing one of the electrical heating units;

.-Fig. 7 is a fragmentary perspective illustrating a slight modification in the arrangement of the coils 'of the electrical heating units shown in Fig. 7 and Fig. 8 is a diagrammatic view illustrating the novel manner in which the electrical heating units are wiredto the mains or supply leads.

. In Fig. 1, there 'are'illustrated three oven sections or units 9 placed one on top of the other and, as shown, supported by a base Specification of Letters Patent. P ented Feb, 14,, 1922 Application filed May 21, 1921. Serial No. 471,381..

formed with a large door opening having a frame 15 of hard .molded asbestos, adapted to be closed by a door 16 preferably hinged at its lov edge at 17.

To gi. the oven sections a finished appearance, to stiffen the same and to provide for nesting the same together, one on top of the other, they are provided at their horizontal upper and lower edges with rigidly secured metallic angle strips 18, and,

at their lower edges, with depending lap strips 19. The lap strips 19 overlap the angles 18 on top of an underlying oven section, as best shown in Fig. 5 but also in Fig. 3. In the arrangement illustrated. the front a light box 20, within which is a light bulb 21. These light boxes 20 are provided with transparent plates 22, (see Fig. 2)-, that perm'it light to be projected intothe oven sections when the bulb is in a closed circuit The circuit to the light bulb 21 includes con- I tacts 23 and 24, (see Figs. 2 and 6). When the oven door is closed, a cam lug 25 thereon engages a spring-pressed plunger. 26 and causes the latter to move the spring contact 99 23 out of engagement with the contact. 24

and thereby open the circuit to the bulb 21;

but when the door opens, the spring-pressed plunger moves and permits the contact 23 to engage the contact 24 and thereby close the bulb circuit. As shown, the plunger 26 is mounted to 'move in a guide 27 in the door frame and through one side of the corresponding light box 20.

The oven doors, as preferably constructed, it!) when the door is closed, will be moved to vertical positions, overlapping the flanges 28, but when the door is turned 'oiitward and downward, the free ends of said stop bars. 29 will drop downward into engagement with Stop brackets or ledges 31 that are engaged by teeth qf latch bolts 36 mounted to slidein. suitable keepers 37 on the free edge of the door, and to be engaged with latch brackets 38 on the upper portion of the fixed door frame, (see Figs. 4 and 5). Obviously, by oscillator movements of the handle 33 and rock 5 aft 32,

the lock bolts 36 can-be moved into and out of the latch brackets38, at will. Gravity will, of course, normally hold the lock bolts engaged with the brackets 38.

lWithin each oven section or unit are eleetrical heating units of: novel construction and arrangement, the pf'et'erred" form there of being illustrated in the drawing. Each such heating unit com rrses a core or bar 39 of insulating mainland, around each' such core, two companion heating wires or coils 40 and 41 wound in substantially paral'lel arrangement and )referably seated in notches formed in the e ges of said core. In

-in the oven in a direction from front to rear the arrangement illustrated in Fig. 7, the wires 40 and 41 are wound parallel with approximately constant spaces between the convolutions thereof, but in Fig. 7, these two wires are wound wi'th progressively increasing distance between the convolutions thereof. The arrangement shown in Fig. 7 is adapted to give greater heat near one end of the element than at the central portion or at the opposite end thereof and, when used in an oven will advisably be placed with the most closely wound end adjacent to the door opening.

The above described heating units maybe made with single piece cores or with sectional rigidly connected cores, as shown in Fig.2. Said units are preferably extended thereof and are laterally spaced substantially as shown in Fig. 2, and they are placed both at the bottom and top' of the oven compartment. The cores 39 at the bottom are rested on supporting rails 42 and l the cores at top are secured to overhead supporting bars 43. The numeral 44 indicates a wire netting, which is placed below and out-"of contact with the upper heating units to protect the same from damage and, as Shown, is detachabLy placed on supporting cleats 45 secured t the side walls of the oven. ,"I

In Fig. 8, the mains or supply wires are maimed by the numerals 46 the 47 m these mains will be connected to the several upper and lower heating units of thepv'en' sections through lead wiresand switches. m.

ranged as diagrammatically illustratedin- Fig. 8, which view shows the wiring of but one of said heating elements but should be treated as switches illustrative of the complete wiring.

i For the lower heating elements of each oven section there is an electric switch 48,

and for the upper heating units of each such oven section is a similar switch49. These switches 48 and 49 are ap lied to the switch 8.0 sections or units, and said switches are'prefl boxes or cabinets 11 of t e respective oven tacts a, Z), c and d. The contact'a is connected by leads 50 to one terminal of'the c oils 41. -The contact I) is connected y a lead 51 to the supply main 46 and a. ad 52 to one terminal of the coil 40 of each heating unit. The contact 0 is connected by a lead 53 to the supply main 47. The contact (Z is connected by a lead 54 to the other terminals of the twocoils 40 and 41 of each heating unit. V a

' By rotation of the rotary elements of the switch, connections across the contacts (1,1),"

0 and cl may be made as follows: In one position, the electricalconnection will be made from the contacts a to b and from c to (Z, and this will close the circuit across; the main or supply line as follows: Thrhugh the lead 51 to the contact 6, thence ito the contact a and through both leads 5Qland 52 and in series through both heating doils '41 and 40 of all of the units to the 1 ad 54., thence from the contact (1 to contac 0 and the lead 53 to the opposite side of te in or supply line. This will conncct 11 multiple all of the lower heating coilsiMO-Qand 41 and will give the greatest possiyllle heat, or, in other words, will connect lip-01 what will be designed high temperature.

In the next position of the switch, only the contacts 0 and (Z will be connected and thenthe circuit across the main r supply line will flow through the lead to the contact c, thence to the contactfd, thence through the lead 54 and fcoil .40 ofleach heating unit, and the lead 52 to thc,,contacts b ahd the lead 51-to the opposite sides of the main or supply line. In this adjustment .of the switch, it will be noted that no current Citllr flOW through the coils 41 of the several heating units, because the contacta has then no electrical connection. with the contact 6.

This will give medium heat because only l30 45 ling switch.

one-half of all of the heating coils-of the complete circuit will then be in action, but

the coils that are in action, nevertheless, will be at high temperature. a

The third ad'ustment of the switch connects the contacts a and c and this connects the heating coils 40 and 41 in series-as folthen in series, will give increased resistance, which will cut downthe current so that the coils will be heated only to low temperature, and will then produce the lowest heat, or, in ,other'words, will be adjusted for low In erature. lime, however, it should be further noted sei eu'al coils or heating wires of any particu la]: heating units are connected 1n series, one

with the other, nevertheless the several complete wires ot the several heating units are not connected in series, one with the other,

' i as Is well known, is of the utmost importance but pre then connected in multiple,

As pr eferably arranged, the so-called coils o heating wires are normally straight wires, .singply wound about a core, and it Wlll be understood that the number of these coils or heating wires may be varied in each heating unit. 1 However, each heating unit preterably comprises a core of non-conducting material and two wires wrapped or coiled about the same in substantially parallel arrangement so thateach wire travel-s a-substantially spiral course nearly or quite from one end to the other of the core.

Very important results are accomplished by the herein described novel arrangement of the elements of the heating units and of the arrangement of the heating units, and the manner of their relative connection, one to the other and to the co-operating control- These improved actions may be stated as follows:

In all of the adjustments of the'switch .above noted, at least one coil or wire of each heating unit of the series controlled by the switch will be inaction and, moreover, such active coil or heating wire of a particular unit will be made hot from end to end of the co-operating core, so that there will be no cold spot in any section or part longitudinally of the core. This gives an exceedingly even distribution of the heat longitudinally of the core, regardless of whether or notone or both of the heating coils or wires is in action, and also gives avery even distribution of heat in a direction transversely of the cores or heating units, because each heating unit always has at least one active coil or heating wire whenever the heat is turned on to the oven. No one heating unit will be hile, for low temperature, the two or between the cores, thus substantially producing as much efi'ective heat between the cores as above the cores. The above action will be more particularly apparent by considering the above 'demediate heat, at which time, one coil or wire of each unit is hot or 1n actlon and the other coil or .wire thereofiscold or out of action. At this time, itwill be noted that jthe hot wire'follows .a winding course between the cold wire, but follows the same vcourse as its companion wire, substantially from end 'to endof the core. With the abovedescribed arrangement, therefore, there are substantially no spots or places throughout the entire zone,'represe nted by the complete series of heating units, that will be materially hotter'than another, and this,

for ood baking.

T e .fourth position of the switch will simply cut connection between all ofthe contacts of the switch so that no current will scribed. adjustment of' the switch for inter flow through any of the coils and, of course, I

heat will then be cut off.

By making the door frame 15 of hard molded asbestos or similar material that is a non-conductor or poor conductor of heat,

radiation of heat from the oven throu h the door opening is reduced to a minimti m.

The operation above described has been assumed to be'that of the heating units at the bottom of the oven, but it will answer also for the description of theaction of the heating elements in' the top of the oven. Of course, in some instances, the top and bottom heating units might beconnected together and operated by a single switch, but

this would not ,be desirablevfor most puroses; Also, it will be understood that the mating elements maybe variously arranged within the oven.

The bread or other thing to be baked will 'usually'be' placed in pans, and to support these pans close to the lower heating ele-, ments without danger of burning, tile blocks 56 or the like are preferably placed on supporting bars 57 secured in the oven just above the lower heating elements. The screen 44 affords no special function except to protect the upper heating elements 'from damage. v

In the baking-of bread and the like,-it-is the common practice tointroduce, at certain times, steam into the hot ovens, and to provide for this, the assembled 0 on sec tions or units are connected by a ste 'm pipe llfi 5'8Jihade up of sections and having valve- 'eqnipped branches 58*" that lead'into the re- 'spective oven-sections. The lowerend' of the j'steam pipe '58 is shown as connected to "'a. steamsupply pipq 59,. which lias a water {trap 60 with a drain cock 61 at the lower end thereof. Here, jibshould be noted that thereto may also be readily. made by pipe sections and fittings of standard length. In Fig. 1, the numeral 62 indicates thermometers for indicating the temperature within the oven sections.

The oven described, being made or built up on the unit plan, may, asis evident. at any time be; readily increased in 'capacity siinplyby adding oven sections or units thereto, and this is made an easy matter by the arrangement. on the unit plan also. of

the various pipe connections, switch boxes and connections and the like that are associated therewith.

The efiicicncy of the oven has been thoroughlydemonstrated in practice.

What I claim is: i

1. A sectional electric oven made up of units, each unit'being a complete ovcn. 2. A sectional electric oven made up of units, each unit being a complete oven, and each unit having upper and lower electrical heating elements and indcpg ndent switches for controlling the same.

3. A sectional electric, ven made up of units, each unit being a inplete oven, and each unit having upper and lower electrical with switches, independent electrical connections between the switches and the heating elements of thefunit, and steam pipe connections to the several units formed in sections corresponding to the units, and each oven unit having its own door and doorlocking and stopping mechanism.

8. A sectional electric oven made up of units, each unit being a complete oven, the oven units having depending edge strips for overlapping underlying unitsand detachably aligning and nesting the units together.

9.- An electrical heating unitcomprising a core and two heating wires applied to said core, in combination with a switch and leads so arranged that. in "one adjustment of said switch, said heating wires will be connected in multiple, in another adjustment of said switch, one of said wires will be in a closed circuit and the other cut out of the closed circuit, and. still another adjustment of said switch, said heating .wires will be connected in series.

a core and two heating wires applied to said core, in combination with a switch and leads so arranged that. in one adjustment of said switch, said heating wires will be connected in multiple, in another adjustment of said switch, one of said wires will be in'a'closed circuit and the other out out ofthe closed .circuit. and. in still another adjustment of said switch, said heating wires will be connected'in series. said two heating wires being coiled about said core substantially from end-to end thereof. and said switch, in a 10. An electrical heating unit comprising fourth position, cutting all of said coiled heatin wires out of circuit.

h a o a ll. An electrical heater comprising a mu]- 40 heating elements and independent switches tiplicity of heating units, each heating unit 4. A sectional electric oven made up of units, each unit being a complete oven, said sections being placed one upon the other and having lapping flanges toraligning and nesting the same together. 7

5. A sectional electric oven made up of units, each unitbeing a complete oven, each unit having its own switch box equipped with switches, and independentelectrical connections between the switches and the heating elements of the unit.

,6. A sectional electric oven made up of units, each unit being a complete oven. each unit having'its own switch box equipped. 'with switches, independent electrical connections between the switches and the heating elements of the unit, and steam pipe connections to the several units formed in sections (airrcsponding to the units.

7. A sectional electric even made up of units, each unit being a complete oven, each unit having its own switch box equipped heating wires of the several units will be; connected in multiple, in another adjust-' ll'lOllt; of said switch, one of the companion wires of each unit will be inthe closed-circuit and the other thereof cutout of the closed circuit, and, in still another adjustment of said switch, the companion wires of the individual units will be connected in series.

12. An electrical heater comprising a multiplicity of heating units, each heating unit having companion heating wires, in combination witha switch and leads s0 arranged that,.in one adjustment of said switch, the

' heating wires of the several units will be connected in multiple, in another adjustment of said switch, one of the companion wires of each unit will be in the closed circuit and the other thereof cut out of the closed cireuit, and, in still another adjustment of said "switch. the companion wires ofthe' individual units will be connected in series, said heating units comprising cores that are hiterally spaced, and the heating wires thereof being'coiled about said cores in substantially parallel arrangement.

13. An electrical heating unit comprisinga core and two heatingwires applied to said core, in combination with a switch and leads so'arranged that, in one adjustment of said switch, said heating wires will be connected in multiple, in another'adjustment of said switch, one of said wires will be in a closed circuit andthe other cat out of the closed circuit, and, in still another adjustment of said switch, said heating wires will be con nected in series, said two'heating wires being coiled about said core substantially from end to end thereof, and said switch, in a fourth position. cutting all of said coiled heatin wires out of circuit, said heating heating companion coils, in combination with a switch and leads arranged so that, in one ad ustment "of said switch, said heating coils will be connected in multiple, in another adjustment of said switch, one of the companion coils will be-in the closed circuit and the other cut out of the closed circuit and, in still another adjustment of said switch, said companion coils will be connected in series, said heating element further comprising a core and said companion coils being wound about the same with a progressively increasing space between the convolution there ofi' 15. A sectional electric oven made up of units, each unit being a complete oven, and

each unit having, upper and lower electricalheating elements and independent switches for controlling the same, said oven units being removably seated, one on top of the other.

16.'A sectional electric oven made up of units, each unit being a complete. oven, and each unit having upper and lower electrical heating elements and independent switches for controlling the same, said oven units being removably seated, one on top of the other and said units further having separable switch boxes.

In testimony whereof I atlix my signature.

ALBERT E. GRAPP. 

